Fix XtraDB to build with atomic operations, for good performance.

The root of the problem is that ./configure mixed together two different things. One is the
availability of GCC atomic operation intrinsics. The other is the selection of which
primitives to use for my_atomic implementation.

Then at some point a hack was made to not use GCC intrinsics in my_atomic to work around
some test failures. But because the two things are mixed in ./configure, this as a side
effect also makes GCC intrinsics unavailable for XtraDB.

Fixed by splitting this in two in configure, so that we have HAVE_GCC_ATOMIC_BUILTINS for
GCC intrinsics availability and MY_ATOMIC_MODE_GCC_BUILTINS for use in my_atomic.

configure.in

@@ -1726,20 +1726,7 @@ then
   fi
 fi
 
-AC_ARG_WITH([atomic-ops],
-	    AC_HELP_STRING([--with-atomic-ops=rwlocks|smp|up],
-	    [Implement atomic operations using pthread rwlocks or atomic CPU
-             instructions for multi-processor or uniprocessor
-             configuration. By default gcc built-in sync functions are used,
-             if available and 'smp' configuration otherwise.]))
-case "$with_atomic_ops" in
-  "up") AC_DEFINE([MY_ATOMIC_MODE_DUMMY], [1],
-                  [Assume single-CPU mode, no concurrency]) ;;
-  "rwlocks") AC_DEFINE([MY_ATOMIC_MODE_RWLOCKS], [1],
-                  [Use pthread rwlocks for atomic ops]) ;;
-  "smp") ;;
-  "")
-    AC_CACHE_CHECK([whether the compiler provides atomic builtins],
+AC_CACHE_CHECK([whether the compiler provides atomic builtins],
 	       [mysql_cv_gcc_atomic_builtins], [AC_TRY_RUN([
   int main()
   {
@@ -1754,13 +1741,31 @@ case "$with_atomic_ops" in
       return -1;
     return 0;
   }
-    ], [mysql_cv_gcc_atomic_builtins=yes_but_disabled],
+], [mysql_cv_gcc_atomic_builtins=yes],
    [mysql_cv_gcc_atomic_builtins=no],
    [mysql_cv_gcc_atomic_builtins=no])])
 
-    if test "x$mysql_cv_gcc_atomic_builtins" = xyes; then
+if test "x$mysql_cv_gcc_atomic_builtins" = xyes; then
   AC_DEFINE(HAVE_GCC_ATOMIC_BUILTINS, 1,
 	    [Define to 1 if compiler provides atomic builtins.])
+fi
+
+AC_ARG_WITH([atomic-ops],
+	    AC_HELP_STRING([--with-atomic-ops=rwlocks|smp|up],
+	    [Implement atomic operations using pthread rwlocks or atomic CPU
+             instructions for multi-processor or uniprocessor
+             configuration. By default gcc built-in sync functions are used,
+             if available and 'smp' configuration otherwise.]))
+case "$with_atomic_ops" in
+  "up") AC_DEFINE([MY_ATOMIC_MODE_DUMMY], [1],
+                  [Assume single-CPU mode, no concurrency]) ;;
+  "rwlocks") AC_DEFINE([MY_ATOMIC_MODE_RWLOCKS], [1],
+                  [Use pthread rwlocks for atomic ops]) ;;
+  "smp") ;;
+  "")
+    if test "x$mysql_cv_gcc_atomic_builtins" = xyes_but_disabled; then
+      AC_DEFINE([MY_ATOMIC_MODE_GCC_BUILTINS], [1],
+                [Use GCC atomic builtins for atomic ops])
     fi
    ;;
    *) AC_MSG_ERROR(["$with_atomic_ops" is not a valid value for --with-atomic-ops]) ;;

include/atomic/nolock.h

@@ -14,7 +14,7 @@
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */
 
 #if defined(__i386__) || defined(_MSC_VER) || \
-    defined(__x86_64__) || defined(HAVE_GCC_ATOMIC_BUILTINS)
+    defined(__x86_64__) || defined(MY_ATOMIC_MODE_GCC_BUILTINS)
 
 #  ifdef MY_ATOMIC_MODE_DUMMY
 #    define LOCK_prefix ""
@@ -22,7 +22,7 @@
 #    define LOCK_prefix "lock"
 #  endif
 
-#  ifdef HAVE_GCC_ATOMIC_BUILTINS
+#  ifdef MY_ATOMIC_MODE_GCC_BUILTINS
 #    include "gcc_builtins.h"
 #  elif __GNUC__
 #    include "x86-gcc.h"